There is interest in a SiC (silicon carbide) semiconductor capable of realizing a higher breakdown voltage, higher current flow and lower on-resistance in comparison with a Si semiconductor. Various kinds of power devices (e.g., diodes and MISFETs) employing the SiC semiconductor are primarily used in systems in the field of power electronics, such as a motor control system and a power conversion system.
Even if a SiC power device has a high breakdown voltage, in some instances the SiC power device suffers from dielectric breakdown when in use. In view of this, different kinds of breakdown voltage measures have been proposed in recent years. For example, in a SiC-Schottky barrier diode including an n-type SiC semiconductor layer and a Schottky electrode Schottky-connected to the SiC semiconductor layer, there is proposed a structure in which a p-type guard ring is formed in the SiC semiconductor layer to make contact with a terminal end portion of the Schottky electrode (see, e.g., JP2008-53418A). In this structure, a depletion layer generated by a p-n junction is broadened near the terminal end portion of the Schottky electrode, thereby alleviating field concentration on the terminal end portion of the Schottky electrode.
Despite the breakdown voltage measure taken by the structure disclosed in JP2008-53418A, there still remains a problem in that current concentration on the terminal end portion of the Schottky electrode may occur at the time of an avalanche breakdown of the device, which leads to the destruction of the device.